This application claims the benefit of Korean Patent Application No. 1999-50512, filed on Nov. 15, 1999, under 35 U.S.C. xc2xa7 119, the entirety of which is hereby incorporated by reference.
1. Field of the invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display (LCD) device and a method of manufacturing the same.
2. Description of Related Art
Of the liquid crystal display devices, an active matrix liquid crystal display (AM-LCD) device, in which the thin film transistors and the pixel electrodes are arranged in the form of a matrix, has lately received special attention due to its high resolution and high performance in displaying moving images.
FIG. 1 is a cross sectional view illustrating a typical LCD device. As shown in FIG. 1, the LCD device includes lower and upper substrates 2 and 4 with a liquid crystal layer 10 interposed therebetween. The lower substrate 2 has a thin film transistor xe2x80x9cSxe2x80x9d (TFT) as a switching element and a pixel electrode 14, while the upper substrate 4 has a color filter 8 and a common electrode 12. The pixel electrode 14 is formed over a pixel region xe2x80x9cPxe2x80x9d and serves to apply a voltage to the liquid crystal layer 10 along with the common electrode 12, and the color filter 8 serves to implement natural colors. A sealant 6 seals an edge of the lower and upper substrate 2 and 4 to prevent leakage of the liquid crystal layer 10.
In order to manufacture the LCD device described above, the upper and lower substrates 4 and 2 are manufactured by a different process, respectively, and are aligned and assembled to each other. However, such a manufacturing process is very complex.
In order to simplify such a manufacturing process, a structure having a color filter formed on the TFT array substrate, hereinafter referred to as simply xe2x80x9ca color filter on TFT (COT) structurexe2x80x9d has been introduced.
FIGS. 2A to 2D are cross sectional views illustrating a process of manufacturing a conventional LCD device having the COT structure. First, as shown in FIG. 2A, a gate electrode 50 is formed on the substrate 1. A gate insulating layer 52 is formed over the whole substrate 1 while covering the gate electrode 50. A semiconductor layer 54 is formed on the gate insulating layer 52. The source and drain electrodes 56 and 58 are spaced apart from each other and overlap both end portions of the semiconductor layer 54, respectively. A passivation film 60 is formed over the whole substrate 1 while covering the source and drain electrodes 56 and 58 and the semiconductor layer 54. The semiconductor layer 54 includes an amorphous silicon layer and 7a doped semiconductor layer. A portion of the doped semiconductor layer between the source and drain electrodes is etched to form a channel region.
Then, the color filter including the color filter layers 62a and 62b of red (R), green (G) and blue (B) are formed over the whole substrate 1. In order to form the three color filter layers of R, G and B, the steps of depositing and patterning a color resin are repeated three times. At this point, a portion of the color filter layer 62a on the channel region xe2x80x9cchxe2x80x9d and a portion of the color filter layer 62b over the drain electrode 58 are etched to be exposed. The reason is to form a light shielding layer and a drain contact hole in a subsequent process.
Subsequently, as shown in FIG. 2C, a light shielding layer 70 is formed to cover the channel region xe2x80x9cchxe2x80x9d, and a planarization layer 64 is formed over the whole substrate 1 while covering the light shielding layer 70. The light shielding layer 70 serves to shield the channel region xe2x80x9cchxe2x80x9d from light and thus is made of an opaque material. Then, portions of the passivation film 60 and the planarization layer 64 are etched to form the drain electrode contact hole 66 on a portion of the drain electrode 58.
Finally, as shown in FIG. 2D, a pixel electrode 68 is formed on the planarization layer 64. The pixel electrode 68 is electrically connected with the drain electrode 58 through the drain electrode contact hole 66.
The method of manufacturing the lower array substrate using the COT technique described above has a high manufacturing yield compared to the method wherein the TFT and the color filter are respectively formed on the different substrates because the pixel electrode and the color filter are easily aligned.
A large-sized LCD device having a high resolution has been recently in great demand. The manufacturing process of a large-sized LCD device has become very complicated, leading to many problems. For example, referring to FIG. 1, in a large-sized LCD device, the upper substrate 4 including the color filter 8 and the lower substrate 2 including the TFTs are manufactured by a different manufacturing process, so that a coefficient of thermal expansion of the two substrates 2 and 4 become different. Thus, an alignment margin between the two substrates 4 and 2 should be considered. In other words, an alignment margin between the lower and upper substrates 2 and 4 is formed due to a difference of the processing temperatures between the two substrates 2 and 4. The processing temperature of the upper substrate 4 is about 220xc2x0 C., while that of the lower substrate 2 is about 300xc2x0 C. The alignment margin is one cause that adversely affects an aperture ratio, as the alignment margins need to be covered by a black matrix for shielding light provided by a light source. As the size of the substrate increases, the aperture ratio also increases. As a result, the required increase in the alignment margins affects the aperture ratio.
When an LCD device is manufactured using the COT technique, there is a disadvantage that the process of forming the passivation film 60 is additionally required. For the foregoing reasons, there is a need for an LCD device having a simplified manufacturing process, a high manufacturing yield, and a high aperture ratio.
To overcome the problems described above, preferred embodiments of the present invention provide a liquid crystal display device having a simplified manufacturing process, a high manufacturing yield, and a high aperture ratio.
A first preferred embodiment of the present invention provides a liquid crystal display device, including: a thin film transistor formed on a substrate, including a gate electrode, a source electrode, and a drain electrode; a color filter overlapping at least one of the source and drain electrodes; a planarization layer formed on the thin film transistor and the color filter; and a pixel electrode formed on the planarization layer and contacting the drain electrode.
The thin film transistor further includes: a gate insulating layer on the substrate and covering the gate electrode; and a semiconductor layer formed on the gate insulating layer, having an amorphous silicon layer and a doped amorphous silicon layer, wherein the gate electrode is formed on the substrate and the source and drian electrode are spaced apart form each other and overlap both end portions of the doped amorphous silicon layer, respectively.
In a second preferred embodiment, the thin film transistor may include an etch stopper on the doped amorphous silicon layer and between the source and drain electrodes.
In a third preferred embodiment, the thin film transistor further includes: an active layer having source and drain regions at both end portions thereof; a gate insulating layer on a central portion of the active layer other than the source and drain regions; a gate electrode formed on the gate insulating layer; and an inter layer insulator formed over the substrate, having first and second contact holes for respectively exposing a portion of the source and drain regions, wherein the source and drain electrodes are formed on the inter layer insulator to respectively contact with the source and drain regions. The active layer can be made of polysilicon. The liquid crystal display device may include a light shielding layer formed between the substrate and the thin film transistor and an insulating layer covering the light shielding layer.
The first preferred embodiment of the present invention provides a method of manufacturing a liquid crystal display device, including: providing a substrate; forming a gate electrode on the substrate; depositing sequentially a gate insulating layer, a pure semiconductor layer and a doped semiconductor layer over the whole substrate; etching the pure semiconductor layer and the doped semiconductor layer to form an active layer, forming source and drain electrodes on the active layer; forming a color filter, the color filter overlapping a portion of the source and drain electrodes; etching a portion of the doped semiconductor layer between the source and drain electrodes to form a channel region; forming a planarization layer over the substrate, the planarization layer including a drain contact hole on a portion of the drain electrode; and forming a pixel electrode on the planarization layer, the pixel electrode electrically contact the drain electrode through the drain contact hole.
The second preferred embodiment of the present invention provides a method of manufacturing a liquid crystal display device, including: providing a substrate, the substrate including first and second regions; forming a thin film transistor on the first region of the substrate, the thin film transistor including a gate electrode, an active layer, and source and drain electrodes; forming a color filter on a second region of the substrate, the color filter overlapping the source and drain electrodes; forming a planarization layer on the thin film transistor and the color filter, the planarization layer including a drain contact hole on a portion of the drain electrode; and forming a pixel electrode on the planarization layer, the pixel electrode electrically contacting with the drain electrode through the drain contact hole. Forming the thin film transistor includes: forming a gate electrode; forming a gate insulating layer, the gate insulating layer covering the gate electrode; depositing a pure semiconductor layer on the gate insulating layer and patterning it to form an active layer; forming an etch stopper on the active layer; depositing a doped semiconductor layer, the doped semiconductor layer covering the pure semiconductor layer and the etch stopper layer; forming source and drain electrodes on the doped semiconductor layer, and etching a portion of the doped semiconductor layer between the source and drain electrodes.
In a third preferred embodiment, the method further includes forming a light shielding layer before forming the thin film transistor; and forming an insulating layer for covering the light shielding layer. The active layer can be made of amorphous silicon. Forming the thin film transistor includes: forming a pure semiconductor layer; forming a gate insulating layer, a width of the gate insulating layer being smaller than the pure semiconductor layer; forming a gate electrode on the gate insulating layer; ion-doping an exposed portion of the pure semiconductor layer to define source and drain regions; forming an interlayer insulator over the substrate, the interlayer including a source region contact hole on a portion of the source electrode and a drain region contact hole on a portion of the drain electrode; and forming source and drain electrodes, the source and drain electrodes electrically contacting with the source and drain regions, respectively. The pure semiconductor layer can be made of polysilicon.
The LCD device having the COT structure according the preferred embodiments of the present invention has the following advantages. Firstly, since the color filter and the TFT are formed on the same substrate, a high aperture ratio can be obtained. Secondly, since an alignment margin between the lower and upper substrates is not required as in the conventional art due to the difference of the processing temperatures between the two substrates, the manufacturing yield is improved. Thirdly, since an additional passivation film is not required, the manufacturing process is simplified.
Advantages of the present invention will become more apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.